The present invention is in the field of polymer chemistry, specifically in the area of methods for rapidly and automatically synthesizing oligomers containing hydroxyacid monomers.
A major focus of current pharmaceutical, chemical and biological research lies in the development of high throughput screening technology in which very large numbers of chemical structures are analyzed for biological activity in automated assay systems. For example, using state-of-the-art robotics, Oncogene Science, Inc. (Uniondale, N.Y.) can screen up to 125,000 compounds a year using one automated system.
The major pharmaceutical and agrochemical companies have developed libraries of millions of different compounds to feed into screening programs. However, with the new screening techniques, the rate determining step in discovering new biologically active molecules is fast becoming the supply of new chemical candidates rather than the assay limitations. For this reason, the search for alternative and improved methods to produce large numbers of compounds for screening has increased.
Natural product discovery, wherein new chemical compounds are extracted from resources such as plants, fungi and microbes is one approach to providing new biologically active molecules. A second approach, often termed "combinatorial," relies on chemical and biological techniques to produce random libraries of compounds from a defined set of building blocks. Methods have been developed which generate: peptide libraries (Houghten, R. A., et al., Nature, 354, 84-86 (1991)), including peptide libraries containing non-natural amino acids (Kerr, J. M., Banville, S. C. and Zuckermann, R. N., J. Am. Chem. Soc., 5, 2529-2531 (1993)); peptoid libraries (Simon, R. J., et al., Proc. Natl. Acad. Sci. USA, 89, 9367-9371(1992)); oligonucleotide libraries (Ecker, D. J., et al., Nucleic Acid Res., 21, 1853-1856 (1993); Ellington, A. D. and Szostak, J. W., Nature, 346, 818-822 (1990)); and oligocarbamate libraries (Cho, C. Y., et. al., Science, 261, 1303-1305 (1993)). Methods for producing oligosaccharide libraries are also being developed (Danishefsky, S. J., et al., Science, 260, 1307-1309 (1993)).
The appeal of the combinatorial approach for generating large numbers of new and varied peptides for screening is readily appreciated by calculating the number of possible combinations of the twenty natural L-amino acids for short peptides. For six-residue peptides (termed hexapeptides) there are 64 million different combinations (20.sup.6), and for seven residue peptides this number increases to 1.28 billion different combinations (20.sup.7). Individually synthesizing 64 million different hexapeptides is impractical. The combinatorial approach to generating new compounds, coupled to an iterative selection process, allows identification of biologically interesting oligomers from a mixture of peptides that are heterogeneous at one or more positions in the peptide. Houghten, et al., Biotechniques, 13, 412-421 (1992), recently reported an iterative selection procedure that identified an antigenic determinant of a peptide recognized by a monoclonal antibody from a library of over 52 million hexapeptides, with approximately 500 assays.
It would be advantageous to create a new class of randomized oligomers in addition to the peptide, peptoid, oligonucleotide, oligocarbamate and oligonucleotide libraries currently being developed.
Natural polymers containing hydroxy acids have been known for a long time, as recently reviewed by M uller, H. -M. and Seebach, D., Ang. Chem. Int. Ed. Engl., 32, 477-502 (1993). These poly(hydroxyacids), termed PHAs, are synthesized by microorganisms for use as storage materials, and have been identified in bacterial membranes and in the tissues of plants and animals (Reusch, R. N. and Sadoff, H. L., J. Bacteriol., 156, 778-788 (1983)). More recently, PHAs have also been detected in human blood plasma where the biopolymer is bound to low density lipoprotein and also to albumin (Reusch, R. N. and Sadoff, H. L., Proc. Natl. Acad. Sci. USA, 85, 4176-4180 (1988)). Certain hydroxyacid dimers also have biological activity. Dimers of (R, R)-hydroxybutyrate act as pheromones in certain species of spiders from the Linyphia family. Schultz, S. and Toft, S., Science, 260, 1635-1637 (1993).
Oligomers of one hydroxy acid, (R)-3-hydroxybutyric acid, have been synthesized by partially degrading/depolymerizing poly[(R)-3-hydroxybutyrate] (PHB), and by polymerizing monomeric derivatives using conventional solution-phase techniques (Seebach, D., et al., Helv. Chim. Acta, 71, 155-167 (1988); Shirakura, Y., et al., Biochim. Biophys. Acta, 880, 46-53 (1986)).
With the availability of new screening techniques, iterative selection processes, and numerous hydroxy acid starting materials, it would be beneficial to have methods for generating random oligomers containing hydroxy acid monomers for biological, chemical and pharmaceutical evaluation.
It is therefore an object of the present invention to provide methods for synthesizing oligomers containing hydroxy acid monomers which can be automated.
It is a further object of this invention to provide methods for creating oligomers containing hydroxy acid monomers which can be used in solution-phase or in solid-phase.
It is another object of the present invention to provide methods for creating oligomers containing hydroxy acid monomers which is simple, rapid, and efficient.
It is a still further object of the present invention to provide a method for synthesizing oligomers containing hydroxy acid monomers which contain biologically active units such as sugars, nucleotides, amino acids, and oliogomers thereof.